The present invention generally relates to contact lenses and more specifically relates to contact lenses having microchannels that promote effective tear fluid exchange.
It has long been recognized that extended wear of contact lenses can lead to corneal complications. Adverse corneal responses to extended contact lens wear are believed to be primarily caused by accumulation of debris trapped at the lens-eye interface.
The cornea is a living tissue with an active metabolism. Waste products, for example lactic acid, carbon dioxide and water, generated by such metabolism must be expelled from the cornea. Contact lens wear results in debris, for example, derived from such waste products, dead epithelial cells, and other materials which are ordinarily removed from the eye, becoming trapped at the lens-eye interface. Such debris, if left to accumulate in the eye, can harm the eye, for example, causing irritation and/or other harm to the eye and/or to the general ocular health of the lens wearer. In order to remain healthy, the cornea must receive an adequate supply of oxygen as the cornea does not receive oxygen from the blood supply as does other living tissue. If sufficient oxygen does not reach the cornea, corneal swelling occurs.
In order to address the problem of oxygen deprivation due to extended wear of contact lenses, hydrophilic lenses with high oxygen transmission properties were developed. Hydrophilic lenses, also sometimes referred to as hydrogel lenses, are soft, flexible water-containing lenses. Clinical studies of hydrophilic lenses have indeed shown a relatively lower degree of corneal swelling in persons wearing such lenses, even when worn over an extended time.
Unfortunately, however, the use of conventional hydrophilic lenses have not eliminated all adverse corneal responses to contact lens wear, in particular extended contact lens wear. For example, conventional hydrophilic lenses do not address the problem of debris accumulation at the lens-eye interface. This suggests that in addition to oxygen permeability, there are other considerations to be addressed in the development of a safe, soft contact lens for extended wear.
One important consideration is effective tear film exchange between the exposed surface of the eye and the surface of the eye covered by the lens. Tear fluids provide for hydration of delicate eye tissue and continuous flushing of debris from the eye. Tear film exchange between the eye and the posterior, i.e. eye facing, surface of a contact lens, is believed to be a critical factor in maintaining eye health. Tear film exchange allows for removal of dead epithelial cells, foreign particulate matter and other debris that may otherwise become trapped between the lens and the eye. It has been hypothesized that increased tear film exchange will not only enhance corneal health but will limit complications such as infection in the eye and microbial keratisis.
Rotation of the lens on the eye has long been recognized as a means of maintaining eye health and comfort. For example, Gordon U.S. Pat. No. 2,989,894 describes a contact lens having five equally spaced, spirally inclined ducts formed on an inner surface of the lens. Each duct is described and shown as extending toward a center of the lens but without extending as far as the corneal region. It is stated that the slow and constant rotation of the lens prevents excess settling of the lens on the cornea. The spiral inclination of the ducts is said to cause the lens to rotate in a clockwise or counterclockwise direction depending upon the direction of inclination.
More recently, Hxc3x6fer et al U.S. Pat. No. 5,166,710 discloses a contact lens having a corneal region that, when placed on the eye, is spaced apart from the corneal surface. Provision is made for causing the lens to rotate upon eye lid blinking action of the wearer. According to Hxc3x6fer et al, lacrimal film is transported along the eye surface as a result of a xe2x80x9cturbo effectxe2x80x9d produced by flattened zones on the lens, which causes the lens to rotate on the eye in response to blinking action. The patent also describes that tear transport may be provided by depressions in the rear face of the lens body. Hxc3x6fer et al shows and describes that the depressions may be depressed portions of the lens body, within the rear surface thereof, the depressions being groove-like or saw tooth-like in shape. Hxc3x6fer et al describes that it is also possible to provide xe2x80x9cthin wave-like curved channelsxe2x80x9d.
Nicolson et al U.S. Pat. No. 5,849,811 discloses a lens material that was developed to provide a balance of oxygen permeability with ion or water permeability, with the permeability being sufficient to provide contact lens xe2x80x9ceye-on movementxe2x80x9d, i.e. movement of the lens on the eye surface.
Each of the patents identified herein is hereby incorporated in its entirety herein by reference.
Despite the advances made in development of comfortable, safe, extended wear contact lenses, there is still a need for an improved contact lens, for example, a lens that promotes tear fluid exchange throughout the surface area of the eye, particularly in the area of the cornea. In addition, there still remains a need for contact lenses which provide enhanced tear fluid exchange.
It has been found that exchange of tear fluid or film from outside the periphery of the lens with tear fluid or film disposed behind the lens, that is between the lens and the eye or at the lens-eye interface, provides for enhanced removal of debris from the lens-eye interface. Such debris removal can result in enhanced ocular health and/or long periods of extended contact lens wear with reduced adverse corneal responses. Enhanced debris removal in accordance with the present invention is particularly useful in combination with contact lenses having high oxygen permeability, such as hydrophilic contact lenses, for example, contact lenses made of hydrophilic polymeric materials, silicone hydrogel materials and the like. A contact lens with effective tear fluid or film exchange, as defined herein, has, generally speaking, substantial positive effect on ocular health. Preferably, the present contact lenses, which are structured and adapted to provide such effective tear fluid or film exchange, have a more significant positive effect on corneal health than a similar contact lens that does not provide effective tear fluid or film exchange.
Contact lenses, for example, extended wear contact lenses, in accordance with the present invention, provide for removal of debris from beneath the contact lens through effective tear fluid or film exchange; provide increased delivery of oxygen to the cornea; and preferably do not depend upon rotation of the lens for promoting the effectiveness of tear fluid or film exchange. The present lenses promote corneal health without significantly adversely effecting wearer comfort or vision. The present contact lenses promote corneal health and wearer comfort and can be economically manufactured using conventional and well known contact lens manufacturing techniques such as, for example, cast molding techniques, machining techniques and the like.
In one broad aspect of the present invention, contact lenses comprise a lens body having a posterior face (as well as a generally opposing anterior face), an optical zone, a peripheral portion, a peripheral edge and a plurality of microchannels as described herein. In one useful embodiment, the microchannels are defined in the posterior face of the lens body, i.e. the surface of the lens that faces the eye surface when the lens is being worn on the eye. The present lenses are particularly adapted as extended wear contact lens, that is lenses which can be worn for a time in a range of about 7 days to about 30 days or more without being removed from the eye. Lenses in accordance with the present invention preferably can be safely and comfortably worn without being removed from the eye for a longer period of time relative to a substantially identical lens without the microchannels.
Advantageously, despite the preferably relatively large number of microchannels in the contact lens of the present invention, the structure and arrangement of the microchannels have substantially no adverse effect on optical zone function, that is on the vision correction ability or property of the optical zone. Thus, the wearer of the present contact lens, with the microchannels as described herein, has substantially the same or better vision quality relative to the same wearer wearing a similar or substantially identical contact lens without the microchannels.
When compared to the channels and ducts in earlier or prior contact lenses, the microchannels in the contact lenses in accordance with the present invention preferably are relatively small in size. For example, each microchannel in accordance with the present invention may have a width of less than about 10 degrees or less than about 5 degrees, and more preferably in a range of about 0.5 degree to about 2 degrees (for example, in a 360 degree substantially circular array).
Each microchannel may be defined by a continuous, substantially non-variable, angular ray extending theoretically from about a periphery of the optical zone of the lens to about an outer periphery of the lens. Preferably, each microchannel has a maximum width in a range of between about 50 to about 500 microns.
Each microchannel may have a maximum depth in a range of about 0.1% to about 90%, more preferably about 10% to about 80%, of the lens thickness. Many contact lenses in accordance with the present invention have lens bodies with thicknesses in the range of about 60 microns to about 90 microns or about 100 microns or about 120 microns.
In an advantageous embodiment, the microchannels are preferably tapered in depth and/or width, with maximum depth and/or width at or about the lens periphery. In other words, the microchannels preferably increase in depth and/or width in a radially outward direction relative to the lens center. The microchannels preferably are substantially straight, rather than curved or wavelike, in form.
A contact lens in accordance with the invention preferably has at least about 5 microchannels, and more preferably, about 10 or about 12 to about 100 or about 200 microchannels. The number of microchannels often depends on the width of the individual microchannels, the spacing between the microchannels and the like factors.
The structure of the lens of the present invention, and in particular, the structure and number of the microchannels, promotes or facilitates a substantially consistent or uniform film of tear fluid between the lens and the eye, that is at the lens-eye interface, and a substantially free flowing tear film at the lens-eye interface. Such substantially consistent or uniform tear fluid film and/or substantially free flowing tear film at the lens-eye interface advantageously facilitates tear fluid exchange between the lens-eye interface and the exposed surfaces of the eye.
As used herein, xe2x80x9cfree flowing tear filmxe2x80x9d refers to the degree of flow or movement of a tear film which is located on a normal mammalian eye, preferably a normal human eye, not associated with a contact lens. A xe2x80x9csubstantially free flowing tear filmxe2x80x9d refers to a degree of flow or movement of a tear film which is at least about 50% or at least about 70% or at least about 80% of the degree of flow or movement of a free flowing tear film.
Because of the relatively large number and/or even distribution of individual microchannels, fluid exchange preferably occurs substantially evenly over the posterior surface of the lens. In effect, the design of the contact lens in accordance with the invention preferably provides for a substantially free flowing film of tear fluid between the contact lens and the eye. When the lens is worn for an extended period of time, the film is continually mixed with tear fluid from other parts of the eye outside the lens periphery. Mixing the tear film from the lens-eye interface, which often contains a substantial amount of debris, with xe2x80x9ccleanxe2x80x9d tear film reduces the debris concentration and thereby allows the lens to be worn for a longer period of time before removal from the eye and/or has an advantageous effect on the ocular health of the lens wearer.
Without wishing to limit the invention to any particular theory of operation, it is believed that the present microchannels facilitate increased tear film exchange by allowing movement of tear fluid from the interior portion of the lens-eye interface to the periphery of the lens and beyond. Upon blinking, the eye lid is believed to exert shear and/or compressive forces on the lens causing displacement and mixing of tear fluid via the microchannels.
In one especially advantageous embodiment of the invention, the plurality of microchannels radiate from the outer edge of the lens optical zone through the peripheral portion of the lens. In this embodiment, the microchannels preferably are dimensioned to be widest and/or deepest, and most distantly spaced apart, at the peripheral edge of the lens. The microchannels run inwardly toward the center of the lens and are most closely spaced together at or about the edge of the optical zone.
In one embodiment, the optical zone preferably is free of microchannels to provide for substantially no interference with the optical zone function or vision correction function of the lens. The optical zone may be disposed somewhat anteriorly, relative to the peripheral portion of the lens, particularly in areas defined between the microchannels. In other words, the optical zone of the lens may be structured to be more distantly spaced apart from the eye relative to the peripheral portion when the lens is being worn on an eye. This anteriorly extending optical zone, combined with the present microchannels, for example, in the peripheral portion of the lens, very effectively provides for useful tear fluid exchange.
In accordance with another feature of the invention, at some of the plurality of microchannels may be extended at least partially into the optical zone, as long as the arrangement of microchannels does not cause substantial interference with vision correction or optical zone function. For example, the arrangement of microchannels may include alternating long and short microchannels with the long microchannels being defined as those that extend into the lens optical zone, and the short microchannels being those that extend from a periphery of the optical zone. The plurality of microchannels may be arranged such that several of the microchannels extend from the center of the lens to the peripheral edge of the lens body edge.
The contact lens in accordance with the invention may include a first set of microchannels within the optical zone and a second set of microchannels within the peripheral portion. The first set of microchannels may have relatively fewer microchannels than the second set of microchannels. The first set and second set may be in fluid communication with each other, for example, by means of an annular microchannel between the first and second sets of microchannels.
The microchannels in the present contact lenses can be provided using any suitable technique or processing or combinations thereof. Preferably, such microchannels are provided during contact lens manufacture using techniques which are conventional and well known in the art. For example, there are at least three opportunities in the process of making contact lens that microchannels can be imparted. These are as follows:
etching the molding insert using etching techniques such as chemical, laser, EDM, photolithograph, UV irradiation, micromachining and the like;
building a relief on a thermoplastic mold using techniques such as microcontact printing and the like; and
imparting the microchannels directly on a lens, such as by lasing (preferred) and the like.
Each and every feature described herein, and each and every combination of two or more of such features, is included within the scope of the present invention provided that the features included in such a combination are not mutually inconsistent.
These and other aspects of the present invention are set forth in the following detailed description, examples and claims, particularly when considered in conjunction with the accompanying drawings in which like parts bear like reference numerals.